Rhiannon is a moderately popular girls' name in United States, ranking #424 in 1999 with 651 recorded births. The name reached its all-time peak in 1999 with 651 births ranking #424. Since 1996, the popularity has increased by 119.2%. In 1999, approximately 1 in every 2,725 girls born was named Rhiannon. STABLE Recent data shows the name is currently stable.